Spontaneous precipitation of calcium silicate hydrate in aqueous solutions

Abstract

Key words calcium silicate hydrate, precipitation, kinetics. PACS 81.10.Dn Calcium silicate hydrates (C-S-H) are very important not only for their contribution to the development of cement and concrete properties but also for use as fillers and in silicate glasses. In the present work, the thermodynamics and the kinetics of the spontaneous precipitation of C-S-H from aqueous solutions were investigated over the pH range 10-12 at 25 °C. The thermodynamic driving force was calculated taking into consideration all equilibria involved in the supersaturated solutions. In the range of the solution supersaturation values examined the precipitation occurred spontaneously, with the exception of the series of experiments done at pH 12.0, where induction times preceded the appearance of the precipitate. The rates were measured at constant pH as a function of the solution supersaturation and were found to depend strongly on the solution supersaturation, pH and on the total calcium to total silicate molar ratio in solution. Fit of the kinetics results in a power law relating rates of precipitation with respect to C-S-H precipitated, suggested a surface diffusion controlled mechanism for the formation of C-S-H. The precipitated solids did not show significant morphological differences at different pH values. From the induction times preceding the spontaneous precipitation at pH 12.0, a value of 30 mJm -2 was calculated for the surface energy of C-S-H.

Preparation of Cement Composites with Ordered Microstructures via Doping with Graphene Oxide Nanosheets and an Investigation of Their Strength and Durability

“…These problems are closely associated with the shape and aggregate state of cement hydration products [9,10,11]. Generally, cement hydration products always have irregular shapes and randomly agglomerate, resulting in the formation of disordered microstructures [12,13,14]. The main solution for reducing the cracks of a cement matrix still mainly depends on filling various fibers and nano mineral materials [15,16,17].…”

Use of graphene oxide nanosheets to regulate the microstructure of hardened cement paste to increase its strength and toughness

“…They produce complex products, such as ettringite (AFt), monosulfate (AFm), calcium hydroxide (CH) and calcium silicate hydrate (C-S-H), which may take rod-like, needle-like or sheet-like crystalline forms, or may be amorphous. 3,4 The crystalline or amorphous structures of the hydration products, and the ways in which these are arranged, form the microstructure of the hardened cement paste, and have an important impact on the mechanical strength of cementbased materials. 5 Therefore, through regulation of this microstructure, it should be possible to achieve significant improvements in the strength and toughness of hardened cement paste, and thereby the cement-based materials derived from it.…”

Physicochemical Impacts of In-Situ Mineralized CaCO3 on Very Early Hydration of Cement at Two Temperatures

“…It is understood that the kinetics of formation of the calcium silicate hydrate gel are sensitive to pH. Higher rates of precipitation have been observed with decreasing pH . The addition of carbon dioxide creates carbonate ions and correspondingly leads to a temporary acidification of the solution .…”